Production of thin steel



Patented Mar. 1, 1927.

' UNITED STATES PATENT OFFICE.

PORTER H. BBACE, OF WILKINSBURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC 80 MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

PRODUCTION OF THIN STEEL.

No Drawing.

I This invention relates-to thin steel sheets,

more particularly to extremely thin sheets which are adapted for use in cores and pole pieces of high-frequency electrical apparatus.

In cases where machinery for the production of high-frequency currents is utilized, as in radio apparatus, it has been found that the ordinary laminations or steel sheets of three to five mils thickness cannot be used successfully on account of the extremely high losses, due to hysteresis and eddy currents, which cause rapid heating of the core or pole pieces, with a great waste of energy and heating of the apparatus, thus greatly decreasing its eiliciency.

All previous attempts to produce very thin steel sheets for this purpose have failed of success. When a pack of steel sheets to be reduced in size is passed through reducing rolls there is a tendency for the formation of a roughened surface thereon. This effect is, apparently, due to the directional properties of the crystals comprising the sheet. The crystals in one sheet, which are oriented in thedirection of-maximum resistance to the rolling stresses, form indentations on the adjacent surface of the contigu-.

ous sheet, resulting in the roughening of all the surfaces, which persists and is intensified as the sheets are reduced in thickness.

In attempting to roll such sheets to very thin sizes, in the neighborhood of two mils or less in thickness, there is a tendency for the sheets to adhere to each other, and perforations appeared in the sheets when their thickness was reduced to about two mils or less.

It is among the objects of the present invention to produce thin steel sheets and to provide a method of producing the same which is eflicient and will result in steel sheets of extreme thinness, the surfaces of which are smooth in which there are no rforations and the cross section of which 15 uniform throu out.

My invention is based on the fact that the metal, when first subjected to cold plas-. tic deformation, such as rolli will "recr stallize on annealing. By choosm a suite 1e annealing temperature the gram sizes of the recrystallized material ma be made much smaller than those of t original metal.

Serial No. 444,989.

In practising my invention, I combine hot rolling of the steel sheet material with cold rolling and annealing in such manner that the grain size of the sheets is kept small relative to the thickness thereof at all stages by hot rolling the pack, then cold rolling the separated individual sheets, subsequently annealing the same in packs to reduce the grain sizes and then rerolling. These steps may be repeated in cycles and the hot rolling may be omitted, if desired, in some of the repeated operations.

A method of producin very thin steel sheets of a thickness of ahout .4; mils is as follows:

A number of sheets of steel are assembled to form a pack which is rolled at a temperature of about 750 to 800 C. to form individual sheets of about five mils in thickness. The edges of the pack are then trimmed, the sheets separated. and cold rolled individually with' the rolls tight together. The sheets are then packed together and hot rolled at a temperature of 700 to 750 C. to produce sheets about three mils thick. The edges of the pack are then trimmed, the sheets separate and cold rolled individually, as before.

The sheets are again packed and then annealed at 700 to 800 0. and cold rolled in the pack to produce sheets about 1.5 mils in thickness. The edges of the pack are then trimmed, the sheets separated and cold rolled individually, as before. The acking, annealing at 700 to 800 C., the su sequent cold rollin to reduce the sheets and rolling the sheets individually cold may be repeated as many times as desired, reducing the thickness of the sheets a desired amount with each cold rolling of the pack. In order to reduce sheets of 1.5 mils to .4 mils in thickness'two cold rollings are usually sufficient.

Although I have described specifically and in detail my invention as applied to the production of steel having a thickness of .4 mils and havestated temperatures and details of manipulation, it is obvious that my invention is not limited to the'exact embodiment described. I may vary the details of manipulation, using various thicknesses and sizes of sheets andI may use temperatures other than those specified. I may perform the Ithe szune,'*-annealing said' pack 0 c 800 C. to reduce the cold rolling.

prises rolling the steel, annealing the same at a temperature of 700 to 800? C. to reduce the grain size and then rolling to further reduce the thickness.

2. 'A method of producing thin steel sheets which comprises rolling the steel, annealing the same to. reduce the grain size and then cold rolling and repeating the process.

A method of producing thin steel sheets which comprises hot rolling a packet sheets, cold rolling-the individual sheets, annealing the same to reduce the grain size and then cold rolling. Y l v i 4. A method of producingthin steel sheets which comprises hot rolling a ack of sheets, cold rollingjthe individual s eets, packing thialsame, annealing said pack, and then cold 1'0 in 5. method of producing thin steel sheets whichcomprises hot rolling a .pack'lof sheets, cold rollingthe individual sheets, cking $309 to grain sizeyand then 6. 'A methodiofproduci'ng thin steel sheets whiclncomprise's hot rolling a 'ack of sheets,

cold rolling theindividu'al-s eets, acking the same, annealing 'said pack at 00 to 800 '.C..to reduce the grain size, separating the sheets and cold rolling the same inthickness.

8. A method of producing thin stee l sheets which comprisesthesteps of reducmgthe thickness-of the sheets by cold rolling in a pack and then annealing at a temperature sufficient to recrystallize the steel and avoid the growth of grains which are large as compared to the thicknessof the sheet.

9.- A method of roducing thinsteel sheets which comprises tlie steps of 'successivelyreducing the thickness of the sheets by cold rolling and then annealing at a temperature suflicientto recrystallize the steel and avoid the growth of grains which arezlarge as compared-to the thickness of the sheet and intermittently cold rolling the individual sheets to prevent unevenness in the surfaces thereof.

10. The method of producing thin steel sheets which comprises the steps of successively cold rolling-the sheets in a pack, heating to a tem erature suflicient to recrystallize the stee but insuflicient to. produce grains which are large in comparison to the thickness of a sheet and smoothing the sheets at intervals by rolling the same individually.

In testimony whereof, I have hereunto subscribed my name this 10th day of February, 1921.

PORTER-H. BRACE. 

